Pyrrolyl–Silicon Compounds as Precursors for Donor–Acceptor Systems Stabilized by Noncovalent Interactions

Abstract

Pyrrolil-silicon compounds were investigated by different theoretical approaches.Model monomers consisted in pyrrole ring N-substituted with silylmethoxy and silylhydroxy end-groups through propyl chain spacer, designated as PySi and PySiOH. Geometrical, vibrational and electronic properties, as well as chemical reactivity, are discussed and compared with Pyrrole (Py) and N-propylpyrrole (N-PrPy) that were studied in parallel for reference purposes and methods validation. The electronic distribution between PySi and PySiOH importantly differs, being the former electron donor, as Py and N-PrPy. Conversely, PySiOH presents donor-acceptor character with LUMO energy level localized on the silanol end-group.Global and local reactivity descriptors predict PySiOH more reactive than PySi with two preferential reactive sites: electron-rich Py ring and electron-deficient silanol group. Based on experimental studies, oligomers of PySiOH linked α−α' via Py rings (α−α'Py n SiOH, n = 2,3) were considered as model molecules of hydrolyzed PySi. The most stable structures were derived from randomly generated α−α'Py n SiOH that were optimized at semiempirical AM1 and refined with M05-2X/6-31G(d,p). Conformational analysis of dimer and trimer structures points to stability enhanced by molecular packing. Nonetheless, NBO and RDG results indicate that oligomers stability is dictated by the cooperative contribution of hydrogen bonding between silanol end-groups and dispersive vdW interactions between silanol and the π system of Py ring.The latter interaction resulting from electron delocalization induced by electron deficient silanol group seems to determine the smaller gap energy of T-shaped OH-π arrangements. The theoretical findings support the peculiar chemical behavior revealed by experiment.

Semiconducting and electrical properties of thin hybrid films from pyrrolyl- and anilynyl-silicon precursors

“…11b). The charge storage/exchange behavior of PySi films is primarily determined by the extent of interpenetration of the σ-π conjugated hybrid network, corroborating previous findings [6,9], while Cu-π(N) interactions play a less important role.…”

“…nitrenium radical cations NH•+ stabilized as zwitte-, prevails in solution and in the condensed phases[2][3][4][5]9]. Conversely, non-covalent OH-π interactions between electron-deficient SiOH and electron-rich pyrrole ring limit the self-condensation of SiOH[1,2,6,9]. The n-type semiconducting behavior of the chemically deposited films corroborates the predilection for cooperative long-range OH-π interactions and charge trapping.…”

“…8a). This is justified by the smaller band-gap of OH-π domor-acceptor complexes that are promoted with hydrolysis [6][7][8][9], leading to an interpenetrated σ-π conjugated hybrid network [6][7][8][9]. Less facilitated is the photo-oxidation of the films deposited using MeOAc solutions (Fig.…”

“…Anilynyl-and pyrrolyl-silicon derivatives (Fig. 1) as precursors of hybrid films to protect Al alloys against corrosion in chloride containing solutions have been widely investigated by our group [1][2][3][4][5][6][7][8][9]. Films with transparent appearance and thicknesses of 2-5 μm are typically obtained by direct-to-metal surface treatment with hydrolyzed methanol-based solutions of PySi and AnSi.…”

“…Hydrolyzed structures of PySi are stabilized by OH-π interactions between electron-rich pyrrole ring and electron-deficient silanol group (SiOH) [1, 2,6,9]. Electropolymerization on inert substrates leads to hybrid films with mixed n-p doping behavior regardless the extent of hydrolysis [7][8][9], indicating that OH-π donor-acceptor complexes and the charge pinning action on pyrrole (Py) ring by silanol (SiOH) are preserved in the hybrid network.…”